Double tap zoom not working on all sites

I could be remembering wrong, but my double-tap zoom feature in the default browser seemed to work pretty much everywhere all of the time. In the last week or so I've noticed it not working more than it does work. I'll tap and tap and tap away in either portrait or landscape and nothing happens. If I tap the bottom right corner of the screen the manual zoom buttons will pop up and I can use them, but no double-tap. I thought it was completely broken, but then I logged on to a forum web-site and it worked there. I've since tested other forum sites and it didn't work there. Anyone else experience this?

Also, in playing with the browser settings I noticed my defualt zoom to be set at medium. Is this everyone's default or is it close?